There are numerous articles of manufacture which advantageously have one or more surfaces which are so-called "non-stick" surfaces, which refers to the ability of such surfaces to resist adhesion of foreign matter. By resisting adhesion, the surface easily releases foreign matter in contact with the non-stick surface. One area in which devices that include a non-stick surface are used frequently is food preparation; the ability of a surface which contacts food during cooking to resist adhesion of the food significantly eases clean-up. Another common application for non-stick surface is in molds for forming an object of a particular configuration. If the mold includes non-stick surfaces, the removal of the molded object is easier, faster, and less likely to damage the article.
To date, articles which require one or more non-stick surfaces in operation generally are produced in one of two forms. The first comprises an article which is formed entirely of non-stick material. Generally such materials are fluoropolymers, such as those sold under the tradenames Teflons.RTM. and Hostaflons.RTM.. Articles so formed have non-stick properties throughout their entire mass, so any scraping or abuse of the surfaces of the article does not significantly reduce the release properties of those surfaces. However, because non-stick materials generally have selectively low mechanical strength, hardness and temperature resistance, the use of these materials is restricted to applications exposed to selectively low mechanical stress and temperature levels.
The second common non-stick form comprises an underlying substrate, such as metal, coated with a non-stick material. Generally the non-stick coating is a polymeric material, such as those described above, or a metal-based coating, such as those sold under the trademark Silverstone.RTM.. Coated articles potentially can withstand higher mechanical stress and temperature than articles integrally formed entirely of non-stick polymers, but are often plagued by chipping, peeling, and leaching of the coating from the article. This is particularly problematic in food preparation, as chipping or peeling of the non-stick coating not only reduces the non-stick properties of the article, but can also cause contamination of the food.
One material type which has received little attention in non-stick application is cement. Cementitious compositions are used to form a wide variety of products, including construction supports, sidewalks, building and decorative tiles, and the like. Generally these compositions comprise a base material, such as Portland cement or calcium aluminate, an inorganic filler, and other additives which influence the physical properties of the composition. Cementitious compositions are attractive to manufacturers and consumers because of their strength, hardness, heat resistance, ease of forming into a desired shape, and relatively low cost.
One limitation of cementitious compositions has been the relatively high surface adhesion of such compositions. This property has limited their use in non-stick applications. One solution offered to improve surface release is to coat a cementitious article with a fluoropolymer coating, see, e.g., U.S. Pat. No. 4,126,475 to Hansen et al., much as is done for other underlying substrates. However, coated cementitious articles are prone to chipping and peeling in the same manner as other coated materials. The prior art fails to disclose a cementitious composition which includes a component mixed throughout the composition which imparts non-stick properties to the material.
It is therefore a first object of the invention to provide a non-stick cementitious composition which can be formed into articles having non-stick surfaces.
It is an additional object of the present invention to provide articles formed from such a cementitious composition.